a history of solar and ultraviolet radiometer calibration ...€¦ · definitions absolute cavity...
TRANSCRIPT
-
A History of Solar and Ultraviolet Radiometer Calibration Standards
Gene Zerlaut and Warren KetolaFranc Grum Memorial Lecture
CORM 2007
-
Genesis of Radiometer Calibration Standards
Applications U. S. Space Program
(1960s – 1975)
Solar Energy Utilization (1975 – 1986)
Materials testing (outdoor exposure testing – more sophisticated indoor testing); ca 1992
Instruments Absolute Cavities
(JPL/Eppley)
Precise solar measure-ments required for product certification
Direct solar and solar ultraviolet irradiance, global hemispherical irradiance
-
Definitions
Absolute Cavity Pyrheliometer: A self-calibrating, electrical-substitution, view-
limited thermopile radiometer the aperture of which is maintained normal to the sun’s beam radiation.
Pyrheliometer: Same as an absolute cavity except that it is not
self-calibrating; i.e., a view-limited radiometer the aperture of which is maintained normal to the sun’s beam component
Pyranometer: A radiometer used to measure all radiation incident
on its flat receiver from a 2-pi steradians hemisphere
-
U.S. Space Program: Impetus for absolute radiometry
Spacecraft borne radiometers used to measure solar radiation from space
One purpose was to more firmly establish the Solar Constant
Absolute cavity pyr-heliometers employed on board spacecraft
The white paint on the parasol used to fixtear in Skylab’s skin was IITRI’s S13G-LO ZnO-pigmented polydimethylsiloxane
-
Absolute Cavity Radiometers: Pyrheliometers
On early satellites to measure the solar constant
Used to calibrate pyranometers and field pyrheliometers for national solar programs (HW & PV)
Used in sophisticated measurement stations for accurate solar irradiance measure-ments
Schematic of a Cavity Radiometer
-
Attributes of an Absolute Cavity Radiometer
Characterized not calibrated
Measurement realized from electrical substitution of emf generated by direct beam radiation
Thermopile alternately receives “heat” from sun-heated cavity and electrical heater Dual cavities and thermopile (center)
of the Eppley HF Absolute Pyrheliometer
-
An IPC held at WMO’s Solar Radiation Center - Davos
International Pyrheliometric Conference (IPC)
-
Non-cavity pyrheliometers being compared at Davos
-
Realization of the World Radiometric Reference (WRR)
WRR Scale maintained by World Standard Group (WSG) WSG Consists of 7
donated Absolute Cavity Pyrheliometers
International Pyrhelio-metric Conferences (IPCs) held every 5 years Always held in Davos,
Switzerland
WRG
1979: WRR Established by 15 Cavities
-
New River Intercomparison of Absolute Cavity Pyrheliometers
NRIPs hosted by DSET Laboratories, New River, Arizona
Funded alternately by SERI and NOAA
Seven NRIPs held from November 1978 to November 1985
34 Instruments from 26 worldwide organi-zations participated
Foreground: DSET’s Eppley Model HF Absolute Cavity Pyrheliometer SN 17142
-
Results of NRIP 7 (Nov. 1985)
-
Intercomparison of Cavities at NREL’s SRRL
The NREL Intercom-parisons are held every 5 yr
Purpose is to
“Bring” the WRR to U.S. after every IPC
Maintain the WRR in the United States between IPCs
-
Intercomparison of Absolute Cavity Radiometers at NREL’s SRRL
-
Solar Collector Testing Drove Need for Standardization
Pyranometers not calibrated periodically exhibited loss in sensitivity – resulting in low irradiance measurements and solar collector efficiency errors (high)
In the early days, manufacturers sought testing laboratories whose efficiency plots were high
NBS, DSET Laboratories Inc. and certain manufacturers led efforts to develop pyranometer calibration standards in ASTM (First in Committee E21 and then E44)
-
Importance to Solar Hot Water Collector Testing
Products sold on basis of efficiency
Efficiency relates to percent of solar energy received that is converted to heat
Efficiency values became very competi-tive in product certifica-tion programs
Hottel-Whillier Governing Equation of a solar HW collector
s
af
LI
ttUKRF
Is = total solar irradiance
-
DSET’s Role in Initiation of Standardization
By 1978, DSET Laboratories had become a major solar thermal collector test laboratory and purchased our first of two Eppley HF Cavity Pyrheliometers.
With support from John Hickey of The Eppley Laboratories, DSET was selected to host the previously mentioned New River Intercomparisons.
Simultaneously, DSET began the commercial calibration of pyranometers and pyrheliometers with the HF Cavity Radiometer as the primary reference DSET was then and is still the only independent, commercial
calibration laboratory recognized as qualified to perform these calibrations.
-
Calibration of a Pyranometer Using a Pyrheliometer - II
Shade-Unshade Method
Reference pyranom-eter is alternately shaded and unshaded
Difference is the direct irradiance
Arguably is more precise than the com-ponent summation method
Shade then unshade
Id cos Z = (VU – VSh) K-1
-
Calibration of a Pyranometer Using a Pyrheliometer - I
Component summa-tion method
Direct plus diffuse equals total
Advantage of this method is ability to calibrate a large number of pyranom-eters simultaneously
Also known as the continuous shade method
Id cos z + ISd = Vt k-1
-
Solar-Initiated Standards Activities (Standard Test Methods)
ASTM Committee E44 on Solar Energy. Formed 1978 (200 members, 10 subcommittees)
E 913-82 Calibration of Reference Pyranometers with Axis Vertical by the Shading Method (Replaced and Withdrawn)
E 941-82 Calibration of Reference Pyranometers with Axis Tilted by the Shading Method (Replaced and Withdrawn)
E 816 (ca 1985) Calibration of Pyrheliometers by Com-parison to Reference Pyrheliometers (Expanded 1990s)
E 824 (ca 1985) Transfer of Calibration from Reference to Field Pyranometers (Expanded and title change 1990s)
-
ASTM E44: Standard reference solar spectral energy distributions
ASTM E 891-87 Tables for Terrestrial Direct Normal Solar Spectral Irradiance for Air Mass 1.5 (Replaced and Withdrawn)
ASTM E 892-87 Tables for Terrestrial Solar Spectral Irradiance at Air Mass 1.5 for a 37-Deg Tilted Surface (Replaced and Withdrawn)
It should be noted that these standard reference spectra were developed by SERI using the “Bright” radiation code
-
International Standardization: ISO TC 180, SC2 on Climate
TC180 was organized in May 1981 with Australia taking the Secretariat
Germany became the Secretariat of SC2 on Climate (DIN)
ASTM E44 calibration standards were a major resource for TC180/SC2
The U.S. was an active participant from start
-
Correspondence Between E44 and ISO/TC180 SC2
ASTM E 816
ASTM E 824
ASTM E 913
ASTM E 941
ASTM E 891
ASTM E 892
ISO 9059
ISO 9847
ISO 9846
Covers E 913 & E 941
ISO 9845-1
Covers E891 & E 892
Calibration Standards
Standard Solar Reference Spectra
-
On January 31, 1986, Congress failed to renew the solar tax credits. As a result the domestic solar hot water industry died in a matter of several days. E44 lingered for a time and then, except for Photovoltaics, Geothermal, and Wind Subcommittees, it became largely inactive.
-
“Weathering” of Materials became an impetus for renewed interest in calibration – under aegis of ASTM G03
In early 1970’s, DSET Laboratories became the first outdoor test lab to monitor weathering effects as a function of accumulated solar and solar ultraviolet radiation
Other testing labs were slow to follow
By late 1980s and early 1990s, other labs and man-ufacturers of accelerated weathering chambers began measurement programs
Exposure test field at DSET north of Phoenix
-
ASTM G03 on Weathering and Durability – SC09 on Radiometry-
In early 1990s, all ASTM E44 calibration and spectral standards were transferred to ASTM G03.09
The G03 standards development program has resulted in several revised and/or new calibration standards
Also, ASTM E 891 and E 892 were withdrawn and replaced.
Atlas’s Everglades Test Laboratory inSouth Miami, Florida
-
Calibration Standards Promulgated by ASTM G03
ASTM E 824-05 Transfer of Calibration from Reference to Field Radiometers Revised to include both pyranometers and UV radiometers (Total
UV, UV-A and UV-B)
ASTM G 167-00 Calibration of a Pyranometer Using a Pyrheliometer Includes horizontal (axis vertical) and any tilt from the horizontal
ASTM G 130-06 Calibration of Narrow- and Broad-Band Radiometers Using a Spectroradiometer
ASTM G 138-96 Calibration of a Spectroradiometer Using a Standard Source of Irradiance With respect to ISO/IEC 17025, there are no sources of accredited
calibrations of “Standard Sources of Spectral Irradiance,” i.e., of standard lamps – independent of NIST, NPL, PTB, etc.
-
Atlas DSET Laboratories
Depicted are:
Calibration of pyra-nometers to E 824 (foreground)
Direct spectral meas-urements – became
G 130 (background)
Absolute direct measurments with Eppley HF Cavity –
E 841 (became G 167) Atlas DSET is the only solar radiometercalibration laboratory accredited to ISO/IEC 17025
-
WRR
IPC X (2005)
NREL
Intercomparisons
Any ACR
IPC = Internat. Pyrheliometric Conference
WRR = World Radiometric Reference
ACR = Absolute Cavity Radiometer
CSM = Component Summation Method
Reference
Pyranometer CSM
Method
Pyrheliometer
Reference
a field radiometer
ASTM G 167 / ISO 9846
G 167 / ISO 9846 G 167 / ISO 9846
ASTM E 816 / ISO 9059
E 816 / ISO 9059
Standards and WRR Traceability: Pyranometers/Pyrheliometers-
-
National Standards Body (e.g.
NIST)
Standard Sources of Irradiance:
Tungsten Halogen & Deuterium
Secondary Standard
Lamps
Commercial
User Standard
Lamps
UV Reference
Radiometers
Spectroradiometer
UV Reference
RadiometersSky-occluded
UV Radiometers
Field
Radiometers Field
Radiometers
Filter Factor
Method
ASTM E 824
ASTM E 824
ASTM G 130
ASTM G 130
ASTM G 138
ASTM G 138
Standards and NIST Traceability: UV Radiometers
-
ASTM G03.09: Transition from E 891/E 892 to G 173/G 177
Since E 891 & E 892 could not be validated, same input parameters were input into SMARTS2 radi-ation codes (Christian Gueymard)
G 173 Reference Solar Spectral Irradiances: Direct Normal and Hemispherical on 37°Tilted Surface
G 177 Reference Solar Ultra-violet Spectral Distributions: Hemis-pherical on 37° Tilted Surface
SMARTS version 2.9.2 Computations for CIE 85 Tab #7
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 2300
Wavelength
W.m
-2.n
m-1
CIE_Tab7_1
CIE_Tab7_2
CIE_Tab7_3
CIE_Tab7_4
CIE_Tab7_5
CIE_Tab7_6
CIE_Tab7_7
CIE_Tab7_8
CIE_Tab7_9
CIE_TAB_7_10
-
Light Measurement in Weathering Tests
Outdoor exposure tests Solar concentrating exposures
How consensus standards were used to resolve major differences in reported UV radiant exposure
Artificial accelerated tests Specifying spectral irradiance Benchmarking against solar UV Resolving an issue with measurement of UVB
irradiance
Problems still to be resolved using consensus standards
-
Solar radiation measurements for outdoor weathering tests
Bandpass
Total solar radiation
Solar UV radiation
Narrow band UV radiation
Applicable standards
For total solar
Calibration: ASTM E824 or E941
Use: ASTM G 183
For solar UV
Calibration: ASTM G 130
Use: ASTM G 183
For narrow band UV
Calibration: ASTM G 130
Use ASTM G 183
ASTM G 130, G 138, and G 183 have been proposed as normative references in ISO DIS 9370
-
The value of solar radiation measurements for outdoor exposures
0
1
2
3
4
5
6
7
8
0 20 40 60 80 100
total days exposed
ch
ain
scis
sio
ns p
er
mo
lecu
le
17-May
26-Aug
11-Sep
Exposure
start date
S = 0.0055 * (radiant exposure)
R2 = 0.954
0
1
2
3
4
5
6
7
8
0 500 1000 1500
Total solar radiant exposure (MJ/m2)
Ch
ain
scis
sio
ns p
er
mo
lecu
le
17-May
26-Aug
11-Sep
Exposure
start date
Chain scission in a degradable polyolefin exposed at different times
Daro, European Polymer Journal,
Vol 26, #1, pp 47-52, 1990
-
Solar Concentrating Exposures
Device description, operation, and use is described in ASTM G 90
MUST measure direct total solar and solar UV
-
Measurement of solar UV on solar concentrating exposures Must determine direct solar UV
In early 1990’s large differences in solar UV reported by two suppliers
Supplier A used calculation based on direct / global ratio for total solar
year
supplier A
total solar
supplier A
solar UV
supplier B
total solar
supplier B
solar UV
Supplier A
UV
percent
Supplier B
UV
percent
1989 61,692 2514 65,400 1833 4.1% 2.8%
1990 59,150 2351 61,637 1743 4.0% 2.8%
1991 56,485 2391 55,904 1564 4.2% 2.8%
1992 51,588 2113 46,250 1233 4.1% 2.7%
1993 59,083 2342 50,688 1357 4.0% 2.7%
-
Measurement of solar UV on solar concentrating exposures Revised ASTM G 90 to specify measurement
procedure for direct solar UV Collimating tube for TUVR radiometer
Better but small design or fabrication differences caused unacceptable variability
Shading disk over TUVR on solar trackerShading disk over TUVR for ASTM G90 direct solar UV
-
Measurement of solar UV on solar concentrating exposures Revised ASTM G 90 to specify measurement
procedure for direct solar UV Collimating tube for TUVR radiometer
Better but small design or fabrication differences caused unacceptable variability
Shading disk over TUVR on solar tracker
year
supplier A
total solar
supplier A
solar UV
supplier B
total solar
supplier B
solar UV
Supplier A
UV
percent
Supplier B
UV
percent
1989 61,692 2514 65,400 1833 4.1% 2.8%
1990 59,150 2351 61,637 1743 4.0% 2.8%
1991 56,485 2391 55,904 1564 4.2% 2.8%
1992 51,588 2113 46,250 1233 4.1% 2.7%
1993 59,083 2342 50,688 1357 4.0% 2.7%
1994 55,661 1405 51,085 1294 2.5% 2.5%
-
Light measurement in artificial accelerated weathering tests
Light sources Carbon-arc, Fluorescent UV, Xenon-arc
Spectral irradiance was only vaguely described From ASTM G26-92
“borosilicate glass inner and outer filter to simulate the spectral power distribution of natural daylight throughout the actinic region”
“suggested minimum spectral irradiance levels are….0.35 W/m2 at 340 nm”
-
Light measurement in artificial accelerated weathering tests
Performance-based standards for artificial accelerated weathering devices
How to specify the spectral irradiance? Absolute specification too restrictive
Too difficult to define / specify measurement conditions
Relative spectral irradiance distribution Collect spectra and express irradiance in
narrow bandpasses as a fraction of broader bandpass
Focus on UV region
-
Specifying spectral irradiance
ASTM G 155 or ISO 4892-2 daylight filters
Table 1— Relative Ultraviolet Spectral Power Distribution
Specification for Xenon Arc with Daylight Filters A,B
SpectralBandpass Wavelength λ in
nm Minimum percent C
Benchmark Solar
Radiation percent D,E,F
Maximum percent C
λ < 290 0.15
290 λ 320 2.6 5.8 7.9
320 < λ 360 28.3 40.0 40.0
360 < λ 400 54.2 54.2 67.5
-
Xenon-arc with daylight filters compared to benchmark solar UV
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
250 275 300 325 350 375 400
wavelength (nm)
Irra
dia
nc
e W
/m2 p
er
nm
ASTM G177 Solar UV Benchmark Spectrum
-
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
280 300 320 340 360 380 400
wavelength (nm)
Irra
dia
nc
e W
/m2 p
er
nm
Xenon-arc with daylight filters compared to benchmark solar UV
ASTM G177 Solar UV Benchmark Spectrum
-
Selecting a solar spectral benchmark
ASTM G 177 compared to CIE 85 Table 4
Atmospheric condition ASTM G 177 benchmark
solar spectrum CIE 85 Table 4 solar spectrum
Ozone (atm-cm) 0.30 0.34
Precipitable water vapor (cm) 0.57 1.42
Altitude (m) 2000 0
Tilt angle 37 facing Equator 0 (horizontal)
Air mass 1.05 1.00
Albedo (ground reflectance) Light Soil wavelength dependent
Constant at 0.2
Aerosol extinction Shettle & Fenn Rural (humidity dependent)
Equivalent to Linke Turbidity
factor of about 2.8
Aerosol optical thickness at 500 nm
0.05 0.10
-
Why is total irradiance in CIE 85 Table 4 higher than G177 benchmark solar?
Tilt angle
CIE 85 Table 4 is horizontal
G 177 is 37o S
Air mass
CIE 85 Table 4 is 1.0
ASTM G 177 is 1.05
air mass
zenith
angle
elevation
angle
1.0 0.00 90.00
1.05 17.75 72.25
Bandpass width CIE 85 Table 4 are 5 nm or non-uniform
ASTM G 177 is 1 nm
Low resolution of CIE 85 Table 4 overestimates integrals
Range of permissible variation in CIE 85 Table 4 integrals by far exceeds the differences between CIE 85 Table 4 and G 177
-
Spectral irradiance comparison CIE 85 table 4* and ASTM G177
0.0
0.5
1.0
1.5
2.0
280 380 480 580 680 780
wavelength (nm)
Irra
dia
nc
e (
W/m
2 p
er
nm
)
CIE85 Table 4
SMARTS2
ASTM G 177
CIE 85 Table 4, 5 nm
* Use CIE 85 table 4 input parameters, calculated with SMARTS2, V2.9.2
-
Spectral irradiance comparison CIE 85 table 4* and ASTM G177
* Use CIE 85 table 4 input parameters, calculated with SMARTS2, V2.9.2
1.0E-10
1.0E-09
1.0E-08
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
280 290 300 310 320
wavelength (nm)
Irra
dia
nc
e (
W/m
2 p
er
nm
)
CIE85 Table 4
SMARTS2
ASTM G 177
CIE 85 Table 4, 5 nm
-
Solving an Irradiance Measurement Issue for Controlled Irradiance Exposures
The problem – inconsistent results for measurement of 310 nm irradiance for controlled irradiance fluorescent UVB exposures
310 nm irradiance set points of 0.49 or 0.71 W/m2
Manufacturer A calibrates their broad band radiometer used to check irradiance and measures correct irradiance in their device with their lamp
Manufacturer A checks device from manufacturer B running at the same set point and measures irradiance that is 30% off
No problem with devices running UVA340 lamps
-
Researching the problem
Spectroradiometer intercomparison
Both manufacturers plus an interested user
Three spectroradiometers
Two fluorescent UV devices
Each with it’s own “calibrator” (reference radiometer)
“Calibrator” calibrated using spectroradiometer per ASTM G130
Calibration transferred to “on board” radiometers used in the exposure device
Two fluorescent UVB313 lamps
One from each manufacturer
-
Intercomparison results
Lamp
set point
wavelength
set point
irradiance
(W/m2)
SR1
(manuf.
A)
SR2
(manuf.
B) SR3
SR1
(manuf.
A)
SR2
(manuf.
B) SR3
UVA340 340 nm 0.89 0.872 0.877 0.856 0.867 0.884 0.866
1.10 1.074 1.083 1.055 1.066 1.086 1.056
UVB313, manuf. A 310 nm 0.49 0.486 0.468 0.471 0.488 0.466 0.488
0.71 0.704 0.678 0.674 0.711 0.675 0.704
UVB313, manuf. B 310 nm 0.49 0.502 0.481 0.501 0.486 0.481 0.476
0.71 0.724 0.699 0.715 0.703 0.695 0.686
Manufacture A device,
manufacturer A calibration
Manufacture B device,
manufacturer B calibration
Excellent agreement between spectroradiometers Maximum difference was 4.4%
-
Intercomparison results
calibrator manufacturer A manufacturer B
device manufacturer A manufacturer B
lamp manufacturer B manufacturer A
310 nm set point (W/m2) 0.71 0.71
calibrator manufacturer A manufacturer B
device manufacturer B manufacturer A
lamp manufacturer A manufacturer B
310 nm set point (W/m2) 0.71 0.71
measured 310 nm irradiance (W/m2) 0.64 0.83
measurement conditions
calibration conditions
A 30% difference when broad band radiometers are calibrated with one lamp and used to measure the other
Why?
-
UVB313 lamp comparison
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
280 290 300 310 320 330 340
wavelength (nm)
no
rma
lize
d irr
ad
ian
ce
(W
/m2 p
er
nm
)
lamp A
lamp B
Significant spectral mismatch
Calibrating a radiometer with one lamp and using it to measure the other lamp leads to errors
Calibrate filter radiometers using a light source with the same spectral irradiance
Adjust calibration for the spectral mismatch
-
Spectral Response Function of a UV-B Radiometer vs Solar Radiation
Integrands from convolution of the spectral response function of a UV-B radiometer with two solar SEDs are disproportionate
Result is a spectral mismatch error in field measurements
This makes it difficult to correlate between sites and between a site and accelerated exposures
Magnitude of errors for UV-A measurements are somewhat less
-
Spectral Mismatch Errors are the Major Contributor to Uncertainty in UV-B Measurements
“a” is total uncertainty
“b” is spectral uncertainty
“c” is angular uncertainty (cosine error)
“d” is temperature effects
720 days of data
Takeshita, Sasaki, Sakata, Miyake & Zerlaut, Eighth Conference on Atmospheric Radiation, 23-28 January 1994, Nashville
-
New Issues for Standardization in ASTM G03
A standard is needed that provides a method for accounting for spectral mismatch between the solar spectrum during calibration and the spectra during measurements in the field
Ultimately, a standard is needed that provides methods for the characterization of pyranometers and UV filter radiometers with respect to: Cosine response (off-angles with respect to direct normal) Temperature response Non-linearity Response time Zero off-set
-
Don’t let this be you…get involved